Summary The goal of this proposal is to discover new factors involved in the age-dependency and spread of Alzheimer?s disease (AD). The main risk factor for AD is old age, but this crucial component has been poorly understood and integrated in modeling the disease. Indeed, the low throughput nature of mouse studies has prevented a systems-level examination of possible molecular causes for the age-dependency of AD. The African killifish, with its naturally compressed lifespan and rapid genome-editing, is ideally suited for systematic discovery and functionally testing of new candidates involved in AD. This proposal will use the African killifish as a model to discover new protein aggregates in old vertebrate brains that could drive AD. Most, if not all neurodegenerative diseases are associated with accumulation of specific protein aggregates (e.g. ?-amyloid and Tau in the case of AD). However, whether other proteins form aggregates and contribute to the disease is not known. Interestingly, recent findings have raised the possibility that some protein aggregates could spread, in a prion-like manner, to drive the progression of neurodegenerative diseases from affected to non- affected regions. Using unbiased proteomics in young versus old killifish, we recently made the tantalizing observation that many proteins form aggregates during normal aging in the brain, and that some of these have the capacity to seed new aggregates, a pre-requisite for potential spreading to different brain regions. To discover new factors that could drive AD with age, we will conduct the following specific aims: 1. Discover new protein aggregates with prion-like seeding activity in the old vertebrate brain; 2. Determine the functional impact of candidate protein aggregates, and their spreading in the brain, on neurodegeneration and cognitive function during aging; 3. Assess how specific interventions influence protein aggregates and prion-like spread; 4. Discover protein aggregates affected by AD genetic risk factors as a function of age. ! So far all AD therapies have failed: this is likely because the dominant risk factor for AD, age, has not been integrated and modeled in vertebrates. Now, for the first time we have the power to do so ? on a proteome-wide scale ? and also to harness a wealth of accumulated knowledge about aging biology. Our approach, in a new genetic model, will provide causative insight, which could have a transformative impact on our understanding of this disease. Results from our experiments, together with collaborations that we have established, will allow us to cover ground quickly and will set the stage for targeted experiments with human AD samples. This interdisciplinary project is ideally suited for discovering new strategies to combat this devastating disease. !